I can't give myself more permissions I can't modify the SA login.
I thought my default my windows BUILTIN account would have access. What am I missing?
Nope.
I'm inferring from the way you stated that, you installed a new SQL Server instance on your local machine. During installation it asks you if you want to provision any administrative accounts, or you can use the default SA account. You would've had to specify your Windows account specifically on that step for it to have SysAdmin access to be able to accomplish the tasks you're trying to do.
It appears your SA account is disabled (as is usually good security practice) and assuming if there's no other Logins provisioned with SysAdmin access, then you'll need to follow these steps to re-enable it, per this StackOverflow answer:
You'll have to use sqlcmd.exe with Windows Authentication (Specify the -E flag) and renable the account:
Open up command prompt and navigate to the SQL Directory and use sqlcmd.exe -S server -E
...
ALTER LOGIN [sa] ENABLE
Note the above steps are ran from the machine of which the SQL Server instance is installed (which in your case is assumptively your local machine).